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Parker describes how all the varieties of humans and animals are easily accounted for by simple Mendelian genetics combining a given built-in array of genes for various traits. The example he gave was of two parents with "medium" or "average" skin color, expressed as AaBb, with the capital letters representing the darkest and the lower case the lightest, saying that EVERY shade of skin that we see on earth can be produced from those two parents, from the darkest African (AABB)to the lightest European (aabb). When you think of every other trait as genetically expressed by the same formula, it becomes clear that an enormous variety of combinations would produce an enormous variety of types or varieties or races -- of people and animals of all kinds -- which would become characteristic of groups as they migrated and became geographically isolated from one another.
What Parker doesn't mention is that this scenario would mean that we would see traits inherited together in large blocks. When you inherit a chromosome from your parent's two copies, you get roughly a single chunk of one copy and two chunk from the other; any traits coded on those chunks stay together. (Put a little more technically, there is roughly one crossover per chromosome arm.) If the Flood happened 180 generations ago, it's easy to estimate how many times each of your chromosomes was broken up as it passed through your ancestors, and thus how large the chunks should be that are inherited together today. They should be about 700,000 base-pairs long on chromosome 1. What we actually see, however, is chunks about 20,000 base-pairs long, a mere factor of 35 wrong.
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So, when it is argued that you don't SEE the signs of a bottleneck that would have occurred at the time of the Flood all you are saying is you don't see the signs that we see occurring NOW, but a bottleneck then would not have produced those same signs. There would have been a lot more genetic diversity left.
Unfortunately, your argument has nothing to do with how bottlenecks are actually detected in genetic data; in fact, you can't detect a bottleneck by measuring the overall genetic diversity. What we actually look at is the frequency of different variants -- how common they are in the population. In your Flood scenario, all variants would be either extremely rare (the result of very new mutations) or pretty common, since even a single copy of a variant at the time of the Flood would have represented 5% of all copies. That looks nothing at all like what we actually see; what we see is a very nice 1/f spectrum, plus an excess of very rare variants caused by the recent human population explosion (of the last 50,000 years or so). Where there
has been a bottleneck, as in the moderate bottleneck in the Out of Africa migration, or the much more severe bottlenecks involved in founding populations like the Finnish, we can easily detect it -- even when it was much longer ago than the alleged Flood bottleneck
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